This invention relates in general to the field of pulse modulation, and in particular to high pulse repetition frequency (PRF) modulation using high power sources.
Modulators are needed in a great number of electronic systems. Pulse modulation, for example, is an integral part of driving magnetron transmitters in radar systems. The need exists in a missile seeker radar system to generate a relatively large amount of radio-frequency (RF) power to achieve required target acquisition ranges. One such program is the Active Radar Target Seeker (ARTS) program.
The ARTS program requires in a small volume a high power modulator which operates at a high PRF, high duty factor, and high efficiency. The high power modulating method needed must produce good fidelity waveforms with low inter-pulse output noise so that return pulses can be received.
A simple two-phase switch will not work in an application such as the ARTS program where a high power magnetron is to be modulated. Using one switch to connect the magnetron to a high voltage supply to generate the RF pulse and the other to clamp it to electrical ground after the pulse does not perform satisfactorily. The equivalent capacitance from components in the circuit such as a magnetron, filament supply, and metal oxide semiconductor field effect transistor (MOSFET) switch must be charged to a high voltage and then discharged every several microseconds or less. The power dissipation at such a high frequency produces a resulting modulating efficiency which is unacceptable from both a power and thermal perspective.
Similarly, a three-channel (phase) switching configuration to drive an ARTS magnetron can be constructed but does not attain the efficiency needed for an application such as the ARTS system. Previous modulator designs have typically suffered at least two major problems: (1) a high PRF does not allow enough time for the circuit to return to its initial conditions before the next pulse period (contributing to excessive noise), and (2) the efficiency of the devices have been low (less than the required minimum of about 70%).